1. Field of the Invention
This invention relates to powder coating compositions especially powder lacquer coating compositions. More particularly, this invention relates to a powder lacquer composition containing at least one 1,2-epoxide compound having at least one 1,2-epoxide group in the molecule which compound has a lower melting point greater than 40.degree. C. which is hardened by a mixture comprising dicyandiamide and an imidazoline derivative. This invention is also concerned with a process of preparing a coating on a substrate wherein a powder coating composition comprising a 1,2-epoxide compound having at least one 1,2-epoxide group in the molecule and having a lower melting point greater than 40.degree. C. is employed together with a hardener composition comprising a mixture of dicyandiamide and an imidazoline derivative.
2. Discussion of the Prior Art
Powder lacquers are finding use to an increasing degree for the manufacture of coatings. Powder lacquers are finely powdered, synthetic compounds, consisting of a resin that is cross-linkable by heating, e.g. epoxide resins, one or more cross-linking agent, i.e. hardener, and additives, such as pigments, dyes, fillers, flow aids and more.
The use of dicyandiamide, as hardener for epoxide-resin powder lacquers, is also known. The use of this conventional hardener leads to the following disadvantage however:
Dicyandiamide has only slight reactivity. Epoxide-resin powder lacquers, that use dicyandiamide as hardener, require longer setting times even at higher setting temperatures (200.degree. C.).
It is furthermore known that cyclic amidines possess a high reactivity in epoxide-resin powder lacquer systems.